The Internet Protocol Multimedia Subsystem (IMS) is an architectural framework that delivers multimedia over an Internet Protocol (IP) transport and uses Session Initiation Protocol (SIP) as a session control protocol. The IMS architecture can be defined according to multiple layers including a user equipment (UE)/device layer, a transport layer, a control layer, and an application (or service) layer.
The control layer of the IMS is made up of various network nodes, including call session control function (CSCF) nodes, media gateway control function (MGCF) nodes, border gateway control function (BGCF) nodes, and other nodes. These network nodes are configured to work together (e.g., by routing packets from one node to another) to provide session control for multimedia sessions that are established over packet networks. This design is quite complex, and it requires significant overhead in computing resources to implement. For example, in a typical voice over IP (VOIP) call flow, a SIP message—as it travels from an origin to a destination—is typically processed, parsed, and inspected by various control layer nodes including an access session border controller (A-SBC), an interconnection SBC (I-SBC), a proxy CSCF (P-CSCF) node, an interrogating CSCF (I-CSCF) node, a serving CSCF (S-CSCF) node, a MGCF node, a BGCF node, a telephony application server (TAS), and multiple application servers (AS's). Moreover, the SIP message is subjected to various queries and evaluation criteria as it traverses these network nodes. Accordingly, today's IMS control layer architecture is suboptimal in terms of its utilization of computing resources and the deployment effort and the operations, administration, and management (OAM) effort that is required to synchronize SIP headers and parameters across the various nodes of the IMS control layer.